1. Technical Field
The present invention relates to a semiconductor device and a method of controlling a semiconductor device.
2. Related Art
A variable resistance storage device (ReRAM: Resistance Random Access Memory) is one type of nonvolatile memory which utilize a change of resistance value of an insulating film provided between electrodes by the application of a voltage. As operation types of ReRAM, there are a unipolar type and a bipolar type. In the unipolar type, any of the state transitions of an increase in the resistance of an insulating film and a decrease in the resistance thereof occurs due to the application of a voltage in the same direction. On the other hand, in the bipolar type, an increase in the resistance of an insulating film occurs due to the application of a voltage in one direction, and a decrease in the resistance of an insulating film occurs due to the application of a voltage in the other direction.
A technique disclosed in Japanese Unexamined Patent Publication No. 2010-15662 relates to a bipolar type ReRAM. Specifically, when the standard electrode potential of an insulating film which is a variable resistance layer is set to Vt, and the standard electrode potentials of a first electrode and a second electrode provided above and below the insulating film are V1 and V2, respectively, the relationships of Vt<V2 and V1<V2 are satisfied. In this case, the above-mentioned technique discloses that the resistance of the insulating film is increased by applying a positive voltage to the second electrode, and the resistance thereof is decreased by applying a positive voltage to the first electrode. In addition, the technique also discloses that a readout operation is performed by applying a positive voltage to the second electrode at the time of readout.
FIG. 22 is a circuit diagram illustrating a typical configuration of a ReRAM cell. As shown in FIG. 22, the ReRAM cell includes a variable resistance device 97 and a selection transistor 98. Here, an upper electrode of the variable resistance device 97 is connected to an interconnect 90, and a lower electrode thereof is connected to an interconnect 94 through a selection transistor 98. When the bipolar type operation is performed, a positive voltage is applied to one electrode in the case of an increase in the resistance, and a positive voltage is applied to the other electrode in the case of a decrease in the resistance. For this reason, it is necessary to connect a switching high-voltage source to both the interconnects 90 and 94.
On the other hand, when the unipolar type operation is performed, both switching operations to decrease the resistance and to increase the resistance are performed by applying a positive voltage to only one of any of the electrodes. For this reason, it is enough to connect the high-voltage source to only either the interconnect 90 or the interconnect 94. Thereby, since a power-supply circuit can be simply designed, there is an advantage that a reduction in the entire area is facilitated at the time of the integration of a memory cell.